Animal models of inflammatory bowel disease: an overview

Inflammatory bowel disease (IBD) research has been performed in human in vitro studies and in in vivo studies using appropriate animal models. Such animal models allow both the examination of inflammatory processes (both early and late events) as well as the evaluation of new therapeutic modalities. Since the first description of the immune complex colitis in rabbits in 1961, overall 63 models have been described, most of which within the last decade. These IBD animal models can be divided into 5 different categories: (1) antigen-induced colitis and colitis induced by microbials; (2) other inducible forms of colitis (chemical, immunological, and physical); (3) genetic colitis models (transgenic and knock-out models); (4) adoptive transfer models, and (5) spontaneous colitis models. In spite of the high overall number of models, none of them is the 'perfect' model and therefore numerous aspects need to be considered when choosing one model for a particular study. Importantly, most clinical aspects (e.g. extraintestinal manifestations or fistula) have recently been described in one or the other model allowing further studies with relevance for almost all aspects of IBD. So far, IBD animal models have taught us important lessons, e.g. the requirement of T-helper cells in most models, the need of a particular genetic background, and the role of the flora in the initiation of IBD. It is expected that our understanding of IBD will further increase in a number of additional areas using animal models, e.g. exploring the role of the innate immune system in IBD.